I live on a streetcar line - I think I can speak to this…
When I moved in, the original oak floor was bare. If you have ever seen the inside of a piano (or even an acoustic guitar, you have seen a sounding board - they are used to amplify the sound produced by the strings.
Oak makes a fantastic sounding board.
There are many “soundproofing” products available, but they all (in my experience) are either limited to a specific frequency (Google ‘MLVB’ - a rather expensive product which promises to reduce sound transmission, but only in the range of human voices.
While this is cheaper and easier to install than the product it is intended to replace (sheet lead - yes, lead - soft, high density stuff - it absorbs sound), it will not do much to cut the sound level.
All other products I’ve seen (ever pay $500 for a Home Depo window?) are either nearly useless or very thick - the windows in question are 30" x 54", and TRIPLE glazed - they each weight well over 100 pounds.
You will not find anything which cuts the noise of a hardwood floor that is less than approx. 4" in thickness - not something you want to put on a floor.
If you wish to pursue this further, the term you need to know is “STC” - Sound Transmission (something) - the massive windows are rated at STC 45 - not “front row at a rock concert”, but it comes close to “1/4 mile from the departure end of the runway at the international airport”.
p.s. - I did not sleep for the first three days of living here, and the first thing I did was to install the thickest carpet on the thickest pad I could afford - that is the noise level of a hardwood floor - the carpeting cut the noise by roughly 30%. I then installed softwood planking on the street side of the living quarters - it did some good, but nowhere near the effect of the carpet and pad.